Recently, a video and audio reproducing apparatus has been used, which reproduces digitized video and audio that are transmitted via a communications line. For example, a moving image distribution system for transmitting moving image data by means of a local area network (a so-called LAN) and other networks such as the INTERNET, etc., and a moving image reproducing apparatus for reproducing moving image data transmitted via a network have been put into practical use.
In such a video and audio reproducing apparatus, for example, in an IP network that carries out data transmission by means of an IP (Internet Protocol), there may be a case where reproduction timing of video and audio lags due to a lag in data transmission time when transmitting packetized video and audio data. Video and audio are synchronized to correspond to such a case. In order to synchronize video and audio, it is common that at least any one of video and audio is delayed by using means for detecting a lag in the receiving time on the basis of time information added to received video and audio data and means for delaying signals to make reproduction timing of the video coincident with that of the audio, whereby the reproduction timing is adjusted to secure synchronization therebetween.
The following procedures for synchronizing video and audio have been conventionally employed:
(1) A delay amount is determined by obtaining a difference in the receiving time between a video packet and a audio packet by the lag detecting means when starting receiving data packets. (2) The delay amount thus determined is set in the delaying means, and hereafter, synchronization is secured by carrying out reproduction while delaying the received data. (3) The delaying amount is re-checked per packet or once every fixed interval in order to execute re-synchronization.
For example, Japanese Published Unexamined Patent Application No. H8-46884 has disclosed a technology for synchronizing video and audio in response to a difference in PTS using respective timing reference signals (PTS) of a video component and a audio component. Also, Japanese Published Unexamined Patent Application No. H9-214936 has disclosed a technology for carrying out re-synchronization by processing refresh process data while permitting delay up to an established permissible value of a processing delay where a decoding process of moving image data delays in response to conditions of a system and requesting refresh process data by clearing the received unprocessed moving image data where the delay exceeds the permissible value of processing delay.
There may be cases where synchronization lags due to a fluctuation in the receiving timing of a data packet during reproduction even if video and audio are once synchronized. As described in the above-described procedure (3), it is necessary to re-synchronize once every fixed interval. However, in prior art synchronizing methods, no device is considered with respect to the re-synchronization timing, wherein there may be cases where, due to discontinuity in reproduction signals when executing re-synchronization, video and audio are interrupted or are subjected to disturbances, and in such cases, viewers feel unnatural or uncomfortable.